Distributed coupling transducer



y 1967 w. J. TROTT DI STHIBUTED COUPLING TRANSDUCER Original Filed Aug.30, 1962 3 Sheets-Sheet 1 L 1 L U INVENTOR WINFIELD JAMES TROTT 3Sheets-Sheet 2 INVENTOR W l N FIELD JAM ES TROTT y 3, 1967 w. J. TROTTDISTRIBUTED COUPLING TRANSDUCER Original Fi led Aug. 30, 1962 W. J.TROTT DI STRIBUTED COUPLING TRANSDUCER May 23, 1967 Original Filed Aug.30, 1962 5 Sheets-Sheet 5 INVENTOR W I N Fl ELD JAM ES TROTT 3,321,738DISTRIBUTED COUPLING TRANSDUCER Winfield J. Trott, Orlando, Fla,assignor t the United States of America as represented by the Secretaryof the Navy Original application Aug. 30, 1962, Ser. No. 220,962, nowPatent No. 3,243,769, dated Mar. 29, 1966. Divided and this applicationSept. 30, 1965, Ser. No. 513,878

2 Claims. (Cl. 340-10) The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

This application is a division of my copending application, Ser. No.220,962, filed Aug. 30, 1962, now Patent No. 3,243,769.

The present invention is directed to underwater transducers forconverting electrical signals to sound or mechanical vibrations and thereverse. More particularly, it concerns transducers which can handle abroad band of frequencies which includes higher frequencies than thoseemployed heretofore.

In order to provide high power projectors in the past, resonanttransducers have usually been employed. The frequency of operation insuch cases was generally determined by the structure of the transducer.The frequency of operation, therefore, could not be altered at will andthe information transmitted was very limited.

An object of the present invention is, therefore, to provide areciprocal transducer for underwater use, which handles high powerlevels efiiciently over a broad band of frequencies.

A further object of the present invention is to provide a reciprocaltransducer of the type described above wherein the mechanical elementsand the electrical elements are arranged to form delay lines which areintercoupled at a plurality of points along their length.

A further object of the invention is to provide a transducer of the typedescribed above wherein the delay lines are periodic in structure.

A further object of the invention is to provide a transducer of the typedescribed above wherein the delay lines are uniform along their length.

These and other objects or attendant advantages of the present inventionare best understood with reference to the following specification inconjunction with the accompanying drawings wherein:

FIG. 1A shows a partly structural, partly schematic representation ofthe electrical and mechanical delay lines used in one embodiment of thetransducer;

FIG. 1B shows a pictorial view of the structure in FIG. 1A;

FIG. 1C shows a second embodiment of the structure in FIGS. 1B and 1A;

FIG. 1D shows the structure of the entire transducer except for theportions depicted in FIGS. 1B and 1C;

FIG. 2 shows a third embodiment of the structure shown in FIG. 1A;

FIG. 3 shows a fourth embodiment of the structure of FIG. 1A andincluding the structure of the electrical delay line which is composedof a semiconductor material; and

FIG. 4 shows a fifth embodiment of the structure shown in FIG. 1A whichemploys magnetostrictive material in the mechanical delay line.

Referring to FIG. 1A, the relationship of the operating portions of thetransducer can be seen. Essentially the transducer is composed of twodelay lines, one electrical and the other mechanical. The two lines arenot independent, however, there being at least one element in eachrepeated line section common to both lines which has both electrical andmechanical properties. In this first em- 3,321,738 Patented May 23, 1967bodiment the common element is a piezoelectric capacitor. If the phasevelocities of the two lines are nearly equal, energy will couplegradually from one line to the other.

The electrical delay line is formed of a plurality of T or pi sections,consisting of series induotances 11 and shut capacitors 10. The sectionsare m-derived using an m equal to The ends of the line are terminatedfirst wth end sections including inductance and capacitor 13 based on anm equal to 0.6 and finally in resistive loads equal to thecharacteristic or image impedance of the line. One load 14 acts as anabsorber to prevent reflections from building up on the line, and theother load is a transmitter or receiver 15 including a series resistor16, if necessary, to provide the image impedance. Many texts contain acomplete analysis of this type of line, as for example, Guillemin,Communication Networks, vol. II, published by John Wiley and Sons, 1935.

The mechanical delay line consists essentially of the capacitors 10which use piezoelectric material as a dielectric. This material isformed in the shape of hollow cylinders which are radially polarized.Each cylinder is provided with an inner electrode 17 and an outerelectrode 18 in the form of coatings which substantially cover thecurved surfaces of the cylinder.

FIG. 1B shows a pictorial view of the mechanical delay line. Thecylinders are cemented end to end with a conducting washer-shaped shield19 interposed between adjacent cylinders. These shields are electricallyconnected to the inner electrodes, but insulated from the outerelectrode either by spacing the electrode from the ends of the cylindersas shown or by coating the fiat surfaces of the shields with a suitabledielectric.

Suitable materials for the various parts are readily available. Theinductances are wound from an appropriate ga-uge of magnet wire and mayinclude an iron core material, if desired. Standard tubular capacitorsoperate satisfactorily at audio frequencies. The newer lead zirconateceramics are preferred as a piezoelectric material although othermaterials such as quartz can be used. The electrodes generally consistof a silver plating or deposit. The shields were made from brassalthough any conducting metal would have served. The cementing agent wasan epoxy resin and the electrical connection between the innerelectrodes and the shields was effected by means of a small solder bead20.

Another similar embodiment of the invention is shown in FIG. 1C. Insteadof separate cylinders this transducer uses a single long hollow cylinder30. The inside of the cylinder is plated with an electrode 33 whichserves as a common current return. The outer surface is plated withseparate bands 32 of current conducting material which serve aselectrodes similar to those shown in FIG. 1A and 1B. The inside of thecylinder is closed by end caps 34 which may be either metal or ceramic.

The operation of this device is similar to that of the embodimentpreviously described, except that radiation takes place from the endcaps of the air filled cylinder. A suitable material for the end caps isberyllium. A member of higher conductivity may be attached to thesurface of the end caps to provide an external terminal for electrode33.

FIG. 1D shows a protective housing which may be used with either of theabove mentioned embodiments. A rigid hollow metal pipe 40 is weldedsecurely to a metal mounting plate 41. A series of apertures or a slot(not shown) is drilled through the plate and pipe at their point oftangency to admit the leads from inductor coils 42, which provide theseries inductance for the electrical delay line. The tops of the coilsare braced by means of a mounting strip 43 connected by wire braces toplate 41. One of the ceramic tubes shown in FIGS. lA-lC is inserted inthe pipe and secured at each end by means of a butyl rubber grommet 47.This grommet grips the tube and pipe at their ends around their entirecircumference, preventing the egress of water between the two whensubmerged. The leads of the coils are attached to appropriate electrodeson the tube by soldering or other electrical connecting means.

To complete the housing structure a metal cover 44 is placed over thecoils and fastened to the plate 41. Suitable gaskets (not shown) may beused to effect a good seal between the two. Leads are connected to thecoils and inner current return electrode of the ceramic tube, and aconventional seal 45 is provided to pass these leads through the covertothe sound transmitter or receiver. A typical model was made using 15sections of one-inch ceramic tube with a 1%. inch inside diameter. Theresponse was substantially flat from 4 kc. to 24 kc. except for a radialmode of resonance in the tube above 15 kc.

FIG. 2 shows still a third embodiment of the ceramic tube structure. Inthis embodiment sections 52 of ceramic tube are enclosed in a stiffmetal pipe 50 with stiff end walls 51. The sections have their axesnormal to that of the pipe and are air filled with stiff end caps. Innerand outer electrodes are connected to the electrical delay line aspreviously described with regard to FIG. 1C. The space between theceramic sections and the met-a1 pipe is filled with oil 53. The metalpipe may be mounted in a housing as shown in FIG. ID, if desired.

FIG. 3 shows a section of a transducer with continuous coupling. Thetransducer consists of a layer of piezoelectric material 60 which may bein the form of a tube as previously described. The lower surface orinside of the tube is plated with a high conductivity layer 61, as forexample, silver. The opposite surface is covered with a layer of mobilecharge type of semiconductor material 62, such as p-type germanium.First and second electrodes 63 and 64 are embedded in this layer atopposite ends of the piezoelectric material. These electrodes aremaintained at a constant potential difference by a D.-C. source 67.

Acoustic signals are transmitted or received by a sonar transceiver unit66. These signals are applied between the first electrode 63 and a thirdelectrode 65 embedded in the semiconductive layer 62 adjacent the firstelectrode. One of the embedded electrodes is held at a fixed potentialwith respect to layer 61, as for example by grounding bot-h electrodeand layer. The complete unit may be mounted in a housing such asdisclosed in FIG. 1D. Electromagnetic waves generated between electrodes63 and 6S diifuse through the semiconductive layer 62 to element 64gradually transferring their energy to mechanical vibration of the layer60. The rate of wave propagation in layer 62 is matched to that in layer60 by varying potentiometer 68.

FIG. 4 shows a magnetostrictive embodiment of the invention. In thisembodiment the series inductances form the common element between theelectrical and the mechanical delay lines. Capacitors 70, which may beof the conventional tubular variety, supply the shunt capacity. Theseries inductance is obtained by a plurality of coils, here representedby one turn each wound in the same sense on the same core. The core ismade of conventional transformer steel, i.e., low carbon with asubstantial percentage of silicon added. The mechanical line requiresprepolarization which may be supplied by permanent magnets 72 insertedin the line or by direct current applied to windings on the core. Soundis radiated or received from the ends of the core including the magnets72.

Various modifications of the invention will be obvious to those skilledin the art. The tubes for example may be square or rectangular ratherthan round. Several transducers may be combined to form a single array,and these transducers may be coupled to a common electrical delay line.In beam steering arrangements where the phase of the transducers isconstantly varying, however, each transducer must have its ownelectrical delay line. 4

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A sound transducer of the type having a mechanical delay line and anelectrical delay line, portions of each of said lines being formed by acommon element capable of reciprocally converting energy betweenelectrical and mechanical forms, said lines having substantially thesame phase velocity whereby energy inserted in one of said lines iscoupled gradually to the other of said lines, comprising:

a layer of piezoelectric material having one side thereof plated with ahighly conductive material;

a layer of mobile charge type of semiconductive material attached to theother side of said layer of piezoelectric material;

first and second electrodes embedded in said layer of semiconductivematerial at widely separated locations;

a third electrode embedded in said layer of semiconductive material at alocation which is between said first and second electrodes but isclosely spaced to said first electrode and a sonar transceiver connectedbetween said first and third electrodes;

whereby when the characteristics of said piezoelectric andsemiconductive layers are such that the propagation velocities ofmechanical and electrical energy respectively in said layers aresimilar, electrical energy applied by the transceiver to said first andthird electrodes will difiuse through said layer of semiconductivematerial and gradually transfer energy and be converted to mechanicalenergy in said piezoelectric layer and conversely mechanical energyapplied to said piezoelectric layer will be converted to electricalenergy and energize said transceiver.

2. A sound transducer as set forth in claim 1 and further including avariable source of potential connected to said first and secondelectrodes for varying the rate of electrical energy propagation in saidlayer of semiconductive material.

References Cited by the Examiner UNITED STATES PATENTS 2,404,391 7/1946Mason 340-10 2,717,981 9/1955 Apstein 333-30 2,815,490 12/1957 DeFaymoreau 333-30 2,898,477 8/1959 Hoesterey 307-885 3,046,500 7/1962Dewitz 33329 3,138,219 6/1964 Blizard 1815 3,254,231 5/1966 Gandhi 33372OTHER REFERENCES -I.R.E. Convention Record, vol. 9 part 6, 1961,Ultrasonic Transducers, by D. L. White, pp. 304-309.

HERMAN KARL SAALBACH, Primary Examiner.

ELI LIEBERMAN, Examiner.

C. BARAFF, Assistant Examiner.

1. A SOUND TRANSDUCER OF THE TYPE HAVING A MECHANICAL DELAY LINE AND ANELECTRICAL DELAY LINE, PORTIONS OF EACH OF SAID LINES BEING FORMED BY ACOMMON ELEMENT CAPABLE OF RECIPROCALLY CONVERTING ENERGY BETWEENELECTRICAL AND MECHANICAL FORMS, SAID LINES HAVING SUBSTANTIALLY THESAME PHASE VELOCITY WHEREBY ENERGY INSERTED IN ONE OF SAID LINES ISCOUPLED GRADUALLY TO THE OTHER OF SAID LINES, COMPRISING: A LAYER OFPIEZOELECTRIC MATERIAL HAVING ONE SIDE THEREOF PLATED WITH A HIGHLYCONDUCTIVE MATERIAL; A LAYER OF MOBILE CHARGE TYPE OF SEMICONDUCTIVEMATERIAL ATTACHED TO THE OTHER SIDE OF SAID LAYER OF PIEZOELECTRICMATERIAL; FIRST AND SECOND ELECTRODES EMBEDDED IN SAID LAYER OFSEMICONDUCTIVE MATERIAL AT WIDELY SEPARATED LOCATIONS; A THIRD ELECTRODEEMBEDDED IN SAID LAYER OF SEMICONDUCTIVE MATERIAL AT A LOCATION WHICH ISBETWEEN SAID FIRST AND SECOND ELECTRODES BUT IS CLOSELY SPACED TO SAIDFIRST ELECTRODE AND A SONAR TRANSCEIVER CONNECTED BETWEEN SAID FIRST ANDTHIRD ELECTRODES; WHEREBY WHEN THE CHARACTERISTICS OF SAID PIEZOELECTRICAND SEMICONDUCTIVE LAYERS ARE SUCH THAT THE PROPAGATION VELOCITIES OFMECHANICAL AND ELECTRICAL ENERGY RESPECTIVELY IN SAID LAYERS ARESIMILAR, ELECTRICAL ENERGY APPLIED BY THE TRANSCEIVER TO SAID FIRST ANDTHIRD ELECTRODES WILL DIFFUSE THROUGH SAID LAYER OF SEMICONDUCTIVEMATERIAL AND GRADUALLY TRANSFER ENERGY AND BE CONVERTED TO MECHANICALENERGY IN SAID PIEZOELECTRIC LAYER AND CONVERSELY MECHANICAL ENERGYAPPLIED TO SAID PIEZOELECTRIC LAYER WILL BE CONVERTED TO ELECTRICALENERGY AND ENERGIZE AND TRANSCEIVER.